Recently, a wireless access system that supports high reliability (HR) compared with a conventional wireless access system is developed. IEEE standard 802.16n that is an amendment to IEEE standard 802.16 and IEEE standard 802.16m is developed as one example of this wireless access system.
For the high reliability, the wireless access system is required to support multi-mode operation where a base station, mobile station or relay station performs a role of the other station, single point of failure (SPOF) immunity for maintaining a communication on the failure of radio link, a direct communication between mobile stations, and a multicast communication. However, a wireless access system for meeting these requirements has not been defined.